PSC lists them in their Brass Casting catalogue. BUT “Out of Stock.” And no plans to cast another run soon. Does anyone know of another firm offering these SP specific items?
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Can you repost this on the Model Railroader part of the forum? You’ll be more likely to get an answer.
The new forums allow anyone in ‘the community’ to edit the group, and I see someone has in fact already changed the group. No need to re-post…
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What is a clam shell?
And is the plow you’re looking for the #39055? Would not one of the Details West or Detail Associates plows be close?
I never gave that a thought. THANK YOU. I’ll sure check them out.
Okay, good luck.
But I’d still like to know what a clam shell is.
Oh, you mean one of these things:
I’ve been trying to find something that explains how those smoke deflectors actually worked, and there isn’t “squat” to be had anywhere, nor a good photograph of them. If they’re supposed to save the engine crew from being smoked out, what good does blowing the smoke straight backwards over the cab do?
Probably because the SP ‘clamshells’ weren’t smoke deflectors, they were stack extenders. ATSF had similar devices that telescoped vertically. They make the stack longer to get better induced draft. Only incidentally do they get it higher enough over the top of the boiler to keep it out of the low-pressure areas along the flanks of the boiler at speed.
Many of the various ‘smoke lifting’ devices over the years were not particularly effective. There were a great many devices, including the early ones by the NRC in Canada that really should have known better, that tried to induce airflow ahead of and around the stack plume that would ‘lift’ it out of the inverted ground effect. They did not, by and large, get it done; the correct answer was either carefully-designed (Witte) or very large (Niagara etc) elephant-ears that created high-pressure vortices along the flanks where forward vision sightlines would be kept open.
The little right-angle caps and pipes, as in the picture of ATSF 3450, were as noted to preclude the effect of exhaust blast on tunnel linings and other overhead surfaces. The problem with that approach was that it ruined much of the actual front-end effectiveness. You may have seen illustrations of engines with long extensions after a right-angle stack cap ‘to pipe the smoke behind the cab in tunnels’. That did not help at typical tunnel speeds and cutoffs…
Well, that explains things, thanks. I’ve seen those pantograph-extended stack extenders on Santa Fe engines and I’ve also seen that long pipe turned horizontally out of the stack and back over the engine towards past the cab, maybe on the great northern around 1910 for the Cascade Tunnel or something.
Ever ridden behind a steam locomotive through a long tunnel? It makes you appreciate all those efforts made way back with the minimization of the smoke hazard.
If you’re going through a tunnel behind anything that uses oxygen and burns fuel of any kind either coal or oil products oxygen deprivation can become a problem regardless of whatever you do to prevent the smoke. Hence why the Cascade tunnel was electrified for decades by the GN. Just look at the 3751 excursion in 91 when she went through a tunnel on techapachi pass slipped the driver’s in a tunnel and steam cleaned 40 years of exhaust off the ceiling of the thing.
Moffat and Rodgers have massive blower systems to provide postive pressure inside the tunnel. So does almost any tunnel over 1 mile long on the highway system. They use massive fans to literally suck the exhaust out at ground level and pull fresh air in at the ceiling.
The more I look at the SP ‘clamshell’, the less I am convinced it is a stack extension and the more I think it is a blast deflector – but on a different principle from what the UP used.
For the latter, we have an interesting page from Don Strack:
Remember that elephant ears were tried in the late Forties on the Big Boys, but not commonly adopted. On the other hand I saw evidence recently that 4014 retains her longitudinally-hinged blast diverted and can use it in tunnels.
What I see in the brass model of the clamshell appears to be the placement of transverse bars to break up any remaining laminar flow in the core of the exhaust jet without actively revectoring it as in the UP’s ‘hoods’. That was (whether rightly or wrongly) suggestive of the arrangement of crossed bars (like a continuation of Goodfellow tips) to induce entraining turbulent flow starting close above the nozzle, with relatively little increase in exhaust back pressure close after release. If someone has a better technical reference or clear pictures of the prototype arrangement, please post a citation or URL.